Arc starting device



Oct. 7, 1941. P. 1.. SPENCER ARC STARTING DEVICE- 2 Sheets-Sheet 1 Filed March 2, 1939 lenn-ms VOLTAGE- CONTROL Oct. 7, 1941. P. L. SPENCER ARC STARTING DEVICE 2 Sheets-Sheet 2 Filed March 2, 1959 SouRc: OF VIBRATOR CURRENT kmlTlNe VOLTAGE CONTROL LOAD INVENTOR. PERCY L. SPENCER BY ATTY.

Patented Oct. 7, 1941 UNITED} STATES PATENT. OFFICE ARC STARTING DEVICE Percy L. Spencer, West Newton, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application March 2, 1939, Serial No. 259,355 '13 Claims. (01. 250-275) This invention relates to a novel igniting electrode arrangement for starting an are spot on a pool type cathode. The igniting electrode is preferably of the electrostatic type which is separated by an insulating wall from the cathode, and initiates an are by means of a high voltage impressed between the cathode and the igniting electrode. In devices of this kind difficulties have been encountered in securing long life. After comparatively short periods of operation, voltages which initially would produce reliable starting were no longer sufficient, and the starting became erratic. This effect became progressively worse until the practical life of the tube terminated.

An object of this invention is to devise an arestarting electrode arrangement of the foregoing type, wherein long life is secured.

Another object, is to increase the sensitivity of the arc-starting arrangement.

A further object is to prevent substantial change in the starting characteristics during life.

The foregoing and other objects of this invention will be best understood from the, following description of exemplifications thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a cross-section of a tube embodying my invention, together with a diagrammatic representation of a circuit with which said tube may be used;

, Fig. 2 is a cross-section taken along line 2- -2 of Fig. 1;

Fig. 3 is an enlarged cross-section of the ignit-' ing electrode; and

Fig. 4 is a view similar to Fig. 1 of another embodiment of my invention.

The tube illustrated in Fig. 1 comprises a sealed envelope I, a pool type cathode 2, preferably consisting of a pool of mercury, and an anode 3. In order to provide means f-or'initiating an are spot on the surface of the cathode pool 2, the tube is provided with an igniting-electrode arrangement 4 consisting of an elongated conductor 5 separated and insulated from the cathode pool 2 by means of an insulating layer 5 covering the surface of said conductor. This insulating coatin or layer is preferably made of glass sealed to the surface of said conductor, preferably as described and claimed in my co-pending application, Serial No. 251,069, filed January 16, 1939, wherein the insulating layer has a thickness of the order of ten mils or less. The conductor 5 has suflicient length and a sufliclently small diameter so that when coated with its insulating layer, it'is sufficiently flexible to move relative to the surface of the pool 2 under the electrostatic forces created between said; pool-'2 and said igniting electrode arrangement by-the application of the igniting voltage impulses, which will be described below. In aparticular embodiment of my invention, I have constructed the conductor 5 of a tungsten wire having a diameter of the order of thirty mils. In order to get an increased length of conductor so as to increase the flexibility or adjust the natural period of vibration thereof, the igniting electrode 4 may be curved as shown more clearly in Fig. 2. The igniting electrode 4 dips down into the pool 2 and contacts the surface thereof at'an angle as shown. The pool 2 and igniting electrode 4 are so related that during any motion between the two which occurs during normal operation, the igniting electrode always engages the surface of said pool. One end of the igniting electrode 4 is supported by a lead-in conductor -1 sealed through the bottom wall of the-envelope I. This support is afforded by having the conductor 5 welded to the upper end of said lead-in conductor 'l. In; order to insulate-and separate the conductor l-from the pool 2, it is covered by an insulating wall 8, also preferably of glass. Since it is desired that the ignition occur at the point where the igniting electrode 4 extends through the surface of the pool 2, the thickness of the glass layer 8 is preferably made substantially greater than that of the glass layer 6. The glass layer 8 may extend up around the joint between the conductors 5 and 1, and may cover all of the surfaces of the conductor (within the envelope I. However, I prefer to leave the upper end of said conductor 1 exposed as illustrated. The exposed end of the conductor 1, therefore, acts as an electrode which facilitates the transition of incipient arc spots formed on the surface of the pool. 2 adjacent the igniting electrode 4 into true are spots. Furthermore, excessive voltages applied between the electrode 7 and the pool 2 cause glow discharges which I believe tend to prevent the building up of voltage surges between the conductor 5 and the pool 2 sufficient to puncture the glass layer 6. External electrical connection may be made to the cathode 2 through a lead-in conductor 9 sealed through the lower wallvof the envelope I and projecting into the pool 2. External electrical connection may 1 also be made to the anode 3 through an anode lead-in l0 sealed through the upper end of the envelope I.

In tubes of the type described above, the application of a comparatively high voltage to the igniting electrode 4 will produce an incipient cathode spot at a point where the igniting electrode 4 is in contact with the surface of the mercury pool 2. If the anode 3 at such a time has impressed upon it a positive voltage, said incipient arc spot will be transformed into a true are spot which will then be maintained by said anode. As previously indicated, I believe that the exposed end of the conductor 1 facilitates this transition of the incipient are spot into a true are. In prior arrangements it has been found that after a comparatively short periodof operation, the starting of the arc spot became erratic and the tube had a short operating life.

I have found, however, that this difficulty can be substantially eliminated by moving the igniting electrode 4 relative to the surface of the mercury pool 2 so as to produce relative motion 'between the insulating layer 6 and the surface of the mercury pool 2 where said insulating layer 6 is'in contact with the surface of said pool, which is where the are spot tends to form. I have found that by producing such a motion, not only is the life of the tube lengthened but also the tube is made more sensitive, and that lower voltages applied to the igniting electrode 4 will produce reliable ignition of the are spot.

As indicated above, the construction described produces such relative motion. An application of a high voltage between the cathode pool 2 and the conductor '5 sets up electrostatic forces which tend to pull down the igniting electrode 4 closer to the surface of said pool. Since, as will be described, the igniting voltage is supplied to the igniting electrode in the form of periodic pulses, such pulses impart mechanical pulsations or vibrations to the igniting electrode 4. This is due tothe fact that, as described, the igniting electrode 4 is sufficiently flexible to move appreciably under the influence of the forces due to suchigniting voltage impulses. In order to secure the maximum of motion at the point where the igniting electrode '4 contacts the surface of the pool 2, said igniting electrode is so proportioned that during its operation it possesses a natural mode of vibration whoseperiodici-ty is equal to the periodicity of the igniting voltage impulses. It is also desirable that the level of the mercury pool 2" be so adjusted with respect to the igniting electrode 4 that a loop of vibration of said electrode 4 occurs where said. igniting electrode contacts the surface 'of said pool By having said electrode 4 in contact with the pool over a considerable length, as indicated substantially between points A and B in Fig.2, it is comparatively simple to cause a loop of vibration to occur somewhere in said length.

i In accordance with my present understand, ing of the theory of operation of these tubes, the novel results secured therefrom are due substantially to the following reasons. I believe that the erratic behavior of the tubes and the termination of the life thereof are due to the contamination of the surface of the insulating layer 6 at the region where the arc spot tends to form. This contamination appears to be due, at least in part, to the accumulation of impurities on the surface of the mercury pool 2. If these impurities are permitted to come into intimate contact with the insulating layer 6, under the action of the arc these impurities attach them-- selves to the surface of the insulating member,

and thus desensitize it. By producing the relative motion described above, stirring of the mercury at the surface of the pool is produced so as to create a stream which carries the impurities away from the insulating layer 6. This action is readily apparent from observing the surface of the mercury pool, provided with an igniting electrode arrangement such as I have described when supplied with igniting impulses of the proper magnitude and frequency. I believe that another factor which contributes to the long life of the tubes constructed in accordance with my invention is that producing the relative motion described, changes in the portion of the electrode 4 in contact with the pool occur which tend to distribute the occurrence of the arc spots along a considerable length of said electrode rather than one particular point along the igniting electrode 4. By distributing the formation of arc spots along the electrode 4, the tendency of the are spot itself to desensitize or destroy the insulating layer 6 is considerably decreased. a 4 g The tube illustrated in Fig. 1 may be utilized in a large number of circuits, one of which is shown diagrammatically; 'Ihecircuit consists of a power transformer [2 having a primary winding I3 connected to a suitable source of alternating current, and a secondary winding l4. One end of the secondary winding is connected to the lead-in I 0, and thus to the anode 3, while the other end of said'secondary winding is connected through a load [5 to the cathode lead 9; An igniting voltage, consisting preferably solely of negative voltage impulses, may be impressed on the igniting electrode 4 from an igniting voltage control l6 energized through the conductors l1, preferably from the same alternating current source as that which supplies the primary winding [3. By supplying igniting voltage impulses of the proper phase to the igniting electrode'4, an arc is initiated during each positive voltage swing of the main anode 3, and thus a controlled discharge current passes between the cathode 2 and the anode 3, which current is in turn delivered to the load 2|.

Although the arrangement shown in Fig. 1

describes one means of moving the igniting electrode relative to the surface of the pool 2, various other means for producing such relative motion may be devised. An example of such an alternative construction is illustrated in Fig. 4. The tube shown therein comprises a sealed envelope IS, a pool type cathode l9, preferably consisting of a pool of mercury, an anode 20 and an igniting electrode 2|. Said igniting electrode consists of a conductor 22 sealed through one end of a side arm 23 formed on the envelope I8. The conductor 22 is separated and insulated from the cathode pool H! by means of an insulating layer 24 covering the conductor 22 as it projects through the surface of the pool [9. This insulating layer 24 is preferably similar to the insulating layer 6, as described in connection with Figs. 1 to 3, inclusive. The conductor 22 is sufiiciently flexible so that the lower end thereof may be vibrated in order to produce the desired relative motion between the insulating layer 24 and the surface of the mercury pool [9. In order to produce this relativemotion, a magnetic armature 25 is mounted upon the conductor 22 within the side arm 23. External to said side arm and adjacent the armature 25 is placed a magnetic core 26 suit-.

ably energized by a magnetizing coil 21. Upon energiaatio'n of the core 26 by the ,coil 21, the armature 25 will be attracted toward said core,

and' thus produce a deflection of the conductor 22, particularly at the lower igniting end thereof. By supplying the coil '2'! with intermittent or pulsating current from a source'of vibratory current 36, the desired vibrations may be imparted to the igniting electrode 2 L The cathode is provided with a suitable-lead-in conductor 28 while the anode is provided with a suitable lead-in conductor 29 in order to establishexternal electrical connections thereto. 'Since the conductoriz is sealed through the-outer end ofthe arm 23, direct electrical connection may ,be made to the outer end thereof.

The circuit shown in Fig, 4 is very similar to that described in connection with Fig. 1. It consists of a power transformer 30 having a primary winding 3| connected to a suitable source of alternating current "andasecon'dary winding 32. One end of the secondary winding 32 is connected to the lead-in conductor 29 of the anode 20. The other end of said secondary winding is connected through a load 33 tothelead-in conductor 28 of the cathode l9. suitable igniting voltage impulses are supplied to the igniting electrode 24 from the igniting voltage control 34 which is energized through conductors35 preferably from the same source of alternating current as that which supplies theprimary'winding 3|. This igniting voltage 24 is connected directly between the lead-in conductor 28 of the cathode l9 and the conductor 22 of the igniting electrode 24. When thearrangem-ent shown in Fig. 4 is energized, arcs are initiated as described in the connection with Fig.1, and the igniting electrode 24 is set in operation by means of the vibratorycura rent supplied fromthe source 36. The relative motion produced between the insulating layer 24 and the surface of the pool l9 produces the various advantageous results described in connection with Fig. 1.

Of course it is to be understood that this ininvention is not limited to the particular arrangements as described above as many equivalents will suggest themselves to those skilled in the art. Various other forms of igniting electrode structure which are immersed in the cathode pool and project through its surface could be used, and various other means of moving said electrodes relative to the surface of the mercury could likewise be devised. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An arc discharge device comprising an anode, a liquid pool cathode, and an elongated flexible igniting electrode structure of the electrostatic type comprising a conductor provided with an insulating wall contacting the surface of said pool, said structure being sufficiently flexible to move under the action of electrostatic forces exerted by an arc igniting voltage between said pool and said electrode to a sufficient extent to cause a flow of the liquid of said pool which carries impurities away from said insulating wall.

2. An arc discharge device comprising an anode, a liquid pool cathode, and an elongated flexible igniting electrode structure comprising a conductor provided with an insulating wall, said structure being supported above said pool at a point substantially displaced from a portion contacting the surface of said pool, said structure being sufliciently flexible for said portion to move under the action of electrostatic forces exerted by an arc igniting voltage between said pool and said electrode to a sufficient extent to cause a flow of the liquid of said pool which carriesimpurities away from-saidinsulating wall.

"'3'. An arc discharge device comprising an anode, a liquid pool cathode, and an elongated flexible igniting electrode structure comprising a conductor provided with an insulating wall, said structure beingsupported above said pool at a point "substantially displaced from a portion contacting the surface of said pool, which portion contactssaid surface at an angle thereto, said structure being sufficiently flexible for said portion to move under the action of electrostatic forces exertedby an arc igniting voltage between said pool and said electrode to a sufficient extent to cause a flow of the liquid of said pool which carries impurities away from said insulating wall.

4. An arc discharge device comprising an anode, aliquid pool cathode, and an elongated flexible igniting electrode structure comprising a conductor provided with an insulating wall,

saidstructure being supported above said pool at a point substantially displaced from a portion contacting the surface of said pool, said structure being sufliciently flexible for said portion to move substantially-under the action of electrostatic forces exerted by an arc igniting voltage between said pool and said-"electrode, and having a natural inode of vibration equal to the frequency ofthe igniting voltage impulses."

5.- An are discharge device comprising an anode, a liquid pool cathode and an elongated flexible igniting electrode structure comprising a conductor provided with aninsulating wall, said structure being'supported above saidpool at a point substantially displaced from a portion contacting the surface of said pool, said structure being sufficiently flexible for said portion to move substantially under the action of electrostatic forc-es exerted by an arc igniting voltage between said pool and said electrode, and having a natural mode of vibration equal to the frequency of the igniting voltage impulses, said structure and pool being so related that said structure contacts said surface substantially in the region of a loop of vibration of said structure.

6. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting electrode element contacting the surface of said pool, and electrostatic means including said electrode element for moving said electrode element relative to said pool at the surface of said pool to a suflicient extent to cause a flow of the liquid of said pool which carries impurities away from said electrode element.

'7. An arc discharge device comprising an anode, a liquid pool cathode, and an elongated igniting electrode structure of the electrostatic type comprising a conductor provided with an insulating wall contacting the surface of said pool, and means for exerting forces on said structure during operation, tending to move the structure relative to the surface of said pool, said structure being sufficiently flexible to move under the action of said forces to a sufficient extent to cause a flow of the liquid of said pool which carries impurities away from said insulating wall.

8. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting structure having an igniting portion in permanent contact with the surface of said pool, and means for exerting forces on said portion during operation, tending to move said portion relative to the surface of said pool, said structure being sufficiently flexible to cause said contacting portion to move relative to the. surface of said pool under theaction of said forces to a sufficient extent to cause a flow of the liquid of said pool which carries impurities away from said contacting portion.

9. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting electrode structure of the electrostatic type having a portion thereof provided with an insulating wall contacting the surface. of said pool, and means for exerting forces on said portion during operation, tending to move said portion relative to the surface of said pool, said structure being sufficiently flexible to cause said contacting portion to move relative to the surface of said pool under the action of said forces to a sufficient extent to cause a flow of the liquid of said pool which carries impurities away from said insulating wall.

10. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting structure having an igniting portion in permanent contact with the surface of said pool, and means for exerting forces on said portion during operation, tending to move said portion relative to the surface of said pool, said structure being sufficiently flexible to cause said contacting portion to move relative to the surface of said pool under the action of said forces to a sufficient extent to cause the firing points on said element to be distributed along a substantial length of said element.

11. An arc discharge device comprising an anode, a liquid pool cathode, and an igniting structure of the electrostatic type having a portion thereof provided with an insulating wall contacting the surface of said pool, means for exerting forces on said portion during operation tending: to move said portion relative to the sur-' face of said pool, said structure being sufficiently flexible to cause said contacting portion to move relative to the surface of said pool under the action of said forces, to a sufficient extent to cause the firing points onsaid element to be distributed along a substantial length of said element.

12. An arc discharge. device comprising an anode, a liquid pool cathode, and an igniting electrode structure, said structure being supported above said pool at a. point substantially displaced from an ignitingportion permanently contacting the surface of said pool, means for exerting forces on said portion during operation, tending to move said portion relative to the surface of said pool, said structure being sufficiently flexible to cause the said contacting portion to move relative to the surface of said pool under the action of said forces,

-13. An arc discharge device comprising an anode, a liquid pool cathode, and an elongated flexible igniting electrode structure of the electrostatic type, comprising a conductor provided with an insulating wall, said structure being supported above said pool at a point substantially displaced from a portion contacting the surface of said pool, said device during; operation having forces acting on said portion, tending to move said portion relative to the surface of said pool, said structure being sufiiciently flexible to cause said contacting portion to move relative to the surface of said pool under the action of said forces.

PERCY L. SPENCER. 

